Anti-bulging container

ABSTRACT

A container (1) of thermoplastic material comprising a side wall (2) and a base (3), said base comprising in a cross section in a plane comprising the container&#39;s vertical axis (A), a concave inwards curved section (4) connected to the side wall (2), at least two successive stairs, each stair consisting of a straight part (5,5&#39;) forming an angle (α1, α2) with a plane (B) perpendicular to said axis (A), followed by a sharp concave outwards curve (6,6&#39;), and a dome (8) consisting of a smooth concave outwards curve, said base (3) being symmetrical about said axis (A).

FIELD OF THE INVENTION

The present invention relates to a container of thermoplastic materialfor containing liquids. The container is designed so as to resistbulging.

BACKGROUND OF THE INVENTION

It is well known in the art to use thermoplastic materials tomanufacture containers for liquids. Some of the liquids to be containedby such containers, for instance bleach-containing compositions, createinternal pressure which builds up with time. In such cases, thecontainers are progressively subjected to deformation due to theinternal pressure build-up, especially at their base. This phenomenon isoften referred to as "bulging". This phenomenon is especially acute inwarm countries where the containers may be exposed to particularlyelevated temperatures. In some instances, bulging can be so severe so asto induce a base deformation which is such that the container can nolonger stay in upright position. For instance in supermarkets, thecontainers may fall of the shelves.

Anti-bulging containers have been disclosed in the art, for instance inDE 16 07 895, DE 21 11 534, EP 0 002 082 and our co-pending EuropeanApplication EP 91202524. These references disclose containers having acentral dome, where the dome is connected to the side walls of thecontainer by pieces of thermoplastic material of various shapes. It istherefore an object of the present invention to provide a container ofthermoplastic material for containing liquids with improved resistanceto bulging.

It is also an object of the present invention to provide a solution tobulging which is particularly applicable to containers of smaller size.

The problem of bulging can to some extent be addressed by increasing thequantity of thermoplastic material used, so as to manufacture acontainer with thick walls. However, this solution is quiteobjectionable from an environmental point of view as well as from anease of manufacturing viewpoint. It is therefore an another object ofthe present invention to provide an anti-bulging container ofthermoplastic material having walls of minimum thickness.

SUMMARY OF THE INVENTION

The present invention is a container (1) of thermoplastic materialcomprising a side wall (2) and a base (3), said base comprising, in across section in a plane comprising the container's vertical axis (A), aconcave inwards curved section (4) connected to the side wall (2), atleast two successive stairs, each stair consisting of a straight part(5,5') forming an angle (α1, α2) with a plane (B) perpendicular to saidaxis (A), followed by a sharp concave outwards curve (6,6'), and a dome(8) consisting of a smooth concave outwards curve. The base (3) of thecontainer (1) is symmetrical about said axis (A).

DETAILED DESCRIPTION OF THE INVENTION

The container according to the invention is made of a thermoplasticmaterial. Such materials have been extensively described in the art andinclude vinyl chloride based resins, polymers and copolymers derivedfrom olefins, acrylic polymers and copolymers, polyethylene,polypropylene, polystyrene, polyethylene terephthalate, polyethyleneterephthalate glycol, or mixtures thereof. The container can be made bysingle or multi layer extrusion of such materials. It can also be madeout of recycled thermoplastic materials. A preferred thermoplasticmaterial for use herein is polyethylene.

The cross section of the container according to the present invention,and/or its base, in a plane perpendicular to the container's verticalaxis (A), can be square or rectangular, ovoid or circular. Furthermore,the base (3) of the container according to the present invention issymmetrical about said axis (A). In a preferred embodiment of theinvention, said cross section is circular. The present invention isparticularly suitable for containers of rather small size, i.e. wherethe container's largest dimension in said cross section is less than 10cm.

The following description refers to FIG. 1 which represents the lowerpart of the container in a cross section in a plane comprising thecontainer's central vertical axis (A). FIG. 2 represents a scale up ofthe lower part of the container, on one side of (A).

The container (1) according to the present invention comprises a sidewall (2) and a base (3). The base (3) which is the gist of the presentinvention is connected to the side wall (2). The base (3) comprises acurved section (4), followed by at least two stairs (5/6,5'/6') and adome (8).

The curved section (4) is connected at one extremity to the sidewall(2), and at the other extremity to at least two successive stairs.The curve of said curved section (4) is concave inwards, i.e. theinterior of said curve faces the inside of the container.

Each stair comprises a straight part (5,5') followed by a sharp curve(6,6'). The straight parts (5,5') can be of same dimensions, but in apreferred embodiment, the straight part which is the closest to theperiphery of the container is longer than straight part which is closestto the center of the container. Each straight part (5,5') forms an angle(α1, α2) with a plane (B) perpendicular to the container's verticalcentral axis (A). According to the present invention, α1 and α2 can bedifferent, but in a preferred embodiment of the invention α1 and α2 arethe same. Each straight part (5,5') is connected to a sharp curve(6,6'). By sharp curve, it is meant herein a curve who's radius issmaller than the radius of the curved section (4), said sharp curves(6,6') are concave outwards, i.e. the interior of each sharp curve(6,6') faces the outside of the container. The radius of the sharpcurves (6,6') can be identical, but in a preferred embodiment, theradius of the sharp curve which is closest to the periphery of thecontainer is larger than the radius of the sharp curve which is closestto the center of the container. In a preferred embodiment of the presentinvention, the base (3) only comprise two stairs.

The sharp curve of the stair which is closest to the center of thecontainer is connected to a dome (8). The dome (8) consists of a smoothcurve. Said smooth curve is concave outwards, i.e. the interior of saidcurve faces the outside of the container. By smooth curve, it is meantherein a curve who's radius is larger than the radius of both curvedsections (6,6').

The present invention is further illustrated by the following example.

EXAMPLE

A cylindrical container according to the present invention is made outof polyethylene. It has a diameter of 90 mm. The radius of the curvedsection (4) is 5.5 mm. The length of the straight part (5) measuredalong plane (B) is 11.5 mm. The radius of the sharp curve (6) is 3 mm.The length of the straight part (5') measured along plane (B) is 4.65mm. The radius of the sharp curve (6') is 2 mm. Finally, the radius ofthe dome is 90 mm. The thickness of the thermoplastic material used forthis embodiment is 1.5 mm throughout the container.

I claim:
 1. A container (1) of thermoplastic material comprising a sidewall (2) and a base (3), said base comprising in a cross section in aplane comprising the container's vertical axis (A), a concave inwardscurved section (4) connected to the side wall (2), at least twosuccessive stairs, each stair consisting of a straight part (5,5')forming an angle (α1,α2) with a plane (B) perpendicular to said axis(A), followed by a sharp concave outwards curve (6,6'), and a dome (8)consisting of a smooth concave outwards curve, said base (3) beingsymmetrical about said axis (A).
 2. A container according to claim 1which has a larger dimension in a cross section in a plane perpendicularto the container's central vertical axis of less than 10 cm.
 3. Acontainer according to claim 1 which has a circular cross section in aplane perpendicular to the container's central vertical axis.
 4. Acontainer according to claim 1 comprising only two stairs
 5. A containeraccording to claim 1 where α1=α2.
 6. A container according to claim 1wherein the straight part (5) which is closest to the periphery of thecontainer is longer than the straight part (5') which is closest to thecenter of the container.
 7. A container according to claim 1 where theradius of the sharp concave outwards curve (6) which is closest to theperiphery of the container is larger than the radius of the sharpconcave outwards curve (6') which is closest to the center of thecontainer.